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    <title>Document</title>
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    <script>
        //声明变量
        let a;
        let b, c, d;
        let e = 100;
        let f = 521, g = 'iloveoyu', h = [];
        //1. 变量不能重复声明
        let star = "张三";
        let star = "法外狂徒";

        //2. 块级作用域   全局,函数,eval
        // if else while for
        {
            let man = "林俊杰";
        }
        console.log(man);

        // 3.不存在变量提升
        console.log(song);
        let song = "那鲁多";

        // 4.不影响作用域链
        {
            let school = '不凡学院';
            function fn(){
                console.log(school);
            } 
            fn();
        }
    </script>
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